Measurement of slider body clearance in a magnetic disk drive using positive and negative electrical pulses

ABSTRACT

A method and system for measuring slider body clearance in a hard disk drive using positive and negative electrical pulses. In one embodiment, at least one positive direct current (DC) pulse is applied between a slider body and a hard disk of the hard disk drive. Furthermore, at least one negative direct current (DC) pulse is applied between the slider body and the hard disk. A contact potential voltage between said slider body and said hard disk is then determined in response to applying the at least one positive direct current (DC) pulse and the at least one negative direct current (DC) pulse.

FIELD OF THE INVENTION

Embodiments of the present invention are related to measurement ofslider body clearances between a slider body and a disk surface of ahard disk drive.

BACKGROUND OF THE INVENTION

Hard disk drives are used in almost all computer system operations. Infact, most computing systems are not operational without some type ofhard disk drive to store the most basic computing information such asthe boot operation, the operating system, the applications, and thelike. In general, the hard disk drive is a device which may or may notbe removable, but without which the computing system will generally notoperate.

The basic hard disk drive model was established approximately 50 yearsago and resembles a phonograph. That is, the hard drive model includes astorage disk or hard disk that spins at a substantially constantrotational speed. An actuator arm or slider is utilized to reach outover the disk. The arm has a head-gimbal-assembly (HGA) composed of asuspension, flexure and a slider carrying the read/write components.

In operation, the hard disk is rotated at a set speed via a spindlemotor assembly having a central drive hub. Additionally, there aretracks evenly spaced at known intervals across the disk. When a requestfor a read of a specific portion or track is received, the actuator andservo-system of the hard drive aligns the head, via the arm, over thespecific track location and the head reads the information from thedisk. In the same manner, when a request for a write of a specificportion or track is received, the hard disk aligns the head, via thearm, over the specific track location and the head writes theinformation to the disk.

Over the years, the disk and the head have undergone great reductions intheir size. Much of the refinement has been driven by consumer demandfor smaller and more portable hard drives such as those used in personaldigital assistants (PDAs), MP3 players, and the like. For example, theoriginal hard disk drive had a disk diameter of 24 inches. Modern harddisk drives are much smaller and include disk diameters of less than 2.5inches (micro drives are significantly smaller than that). Advances inmagnetic recording are also primary reasons for the reduction in size.

As the data storage industry constantly strives to improve data storagedensity, it is becoming increasingly important to reduce the clearanceof slider assembly over the surface of the magnetic disk. However, asthe slider-to-disk spacing becomes smaller than 10 nanometers (10 nm),the electrostatic and intermolecular forces between the slider and diskbecome increasingly significant. Therefore, a need exists fordetermining localized contact potential voltages and localized clearancedata between a slider body and a hard disk of a hard disk drive.

However, the small drives have small components with very narrowtolerances. Disk drive sliders are designed to fly in very closeproximity to the disk surface. For instance, in some systems slider maybe designed to fly only three to five nanometers above the disk surface.In a system with such close tolerances, components can be subject to vander Waals, Meniscus, electrostatic, spindle motor charge up, and contactpotential forces. These forces are due to a variety of causes, such as:the molecular attraction of components in very close proximity; adhesivefriction caused by contact between the slider and the lubricant on thedisk; the build up of electrical potential between the disk and theslider caused by the rotating disk surface (tribo-charging); the buildup of electrical potential in motor bearings (tribo-charging); potentialdifference that exists between two different metals (different Fermilevels of slider and disk material); and impacts between the slider anddisk surface. These forces alone, and in combination, create bouncingvibrations in the slider that can cause media damage and can also causedata loss during read and write operations.

SUMMARY OF THE INVENTION

A method and system for measuring contact potential in a hard disk driveusing positive and negative electrical pulses. In one embodiment, atleast one positive direct current (DC) pulse is applied between a sliderbody and a hard disk of the hard disk drive. Furthermore, at least onenegative direct current (DC) pulse is applied between the slider bodyand the hard disk. A contact potential voltage between said slider bodyand said hard disk is then determined in response to applying the atleast one positive direct current (DC) pulse and the at least onenegative direct current (DC) pulse.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the present invention and,together with the description, serve to explain the principles of theinvention. Unless specifically noted, the drawings referred to in thisdescription should be understood as not being drawn to scale.

FIG. 1 is a perspective view of an exemplary hard disk drive.

FIG. 2 shows an exemplary electrostatic field that exists between aslider body and a hard disk of a hard disk drive.

FIG. 3 shows in greater detail the relationship between a slider bodyand a hard disk of a hard disk drive.

FIG. 4 shows a system for determining localized contact potentialvoltages and localized clearance data between a slider body and a harddisk of a hard disk drive.

FIGS. 5A and 5B show exemplary bias voltages applied to discreetlocations of a hard disk in accordance with embodiments of the presentinvention.

FIGS. 6A and 6B are graphs showing the clearance of a slider bodyrelative to a hard disk in response to variations in an applied biasvoltage in accordance with embodiments of the present invention.

FIG. 7 is a graph showing the voltage pulses applied at variousamplitudes to detect contact between a slider body and a hard disk inaccordance with embodiments of the present invention

FIG. 8 is a flowchart of a method for measuring contact potential in ahard disk drive using positive and negative electrical pulses inaccordance with embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. While the present invention will be described in conjunctionwith the following embodiments, it will be understood that they are notintended to limit the present invention to these embodiments alone. Onthe contrary, the present invention is intended to cover alternatives,modifications, and equivalents which may be included within the spiritand scope of the present invention as defined by the appended claims.Furthermore, in the following detailed description of the presentinvention, numerous specific details are set forth in order to provide athorough understanding of the present invention. However, embodiments ofthe present invention may be practiced without these specific details.In other instances, well-known methods, procedures, components, andcircuits have not been described in detail so as not to unnecessarilyobscure aspects of the present invention.

With reference now to FIG. 1, a schematic drawing of one embodiment of amagnetic hard disk file or drive 100 for a computer system is shown.Drive 100 has an outer housing or base 113 containing a disk pack havingat least one media or magnetic disk 102. The disk or disks 102 arerotated (see arrows 141) by a spindle motor assembly having a centraldrive hub 117. An actuator comprising a plurality of parallel actuatorarms 105 (one shown) in the form of a comb that is movably or pivotallymounted to base 113 about a pivot assembly 123. A controller (not shown)is also mounted to base 113 for selectively moving the comb of arms 105relative to disk 102.

In the embodiment shown, each arm 105 has extending from it at least onecantilevered load beam and suspension 106. A magnetic read/writetransducer or head is mounted on a slider 101 and secured to a flexurethat is flexibly mounted to each suspension 106. The read/write headsmagnetically read data from and/or magnetically write data to disk 102.The level of integration called the head gimbal assembly (HGA) is headand the slider 101, which are mounted on suspension 106. The slider 101is usually bonded to the end of suspension 106. The head is typicallypico size (approximately 1245×1000×300 microns) and formed from ceramicor intermetallic materials. The head also may be of “femto” size(approximately 850×700×230 microns) and is pre-loaded against thesurface of disk 102 (in the range two to ten grams) by suspension 106.

Suspensions 106 have a spring-like quality, which biases or urges theair-bearing surface of the slider 101 against the disk 102 to cause theslider 101 to fly at a precise distance from the disk. An actuator 104(e.g., a voice coil motor) is also mounted to arms 105 opposite the headgimbal assemblies. Movement of the actuator 104 by the controller movesthe head gimbal assemblies along radial arcs across tracks on the disk102 until the read/write transducer is positioned above the desired datatrack. The head gimbal assemblies operate in a conventional manner andtypically move in unison with one another, unless drive 100 usesmultiple independent actuators (not shown) wherein the arms can moveindependently of one another.

FIG. 2 shows in greater detail, the electrostatic interaction betweenslider body 101 and magnetic disk 102. In operation, magnetic disk 102rotates from right to left with respect to slider body 101 (e.g.,typically shown as arrow 203). Enlargement 204 of the slider/diskinterface shows lines representing an electric field 205 that is formedfrom a potential difference between slider body 101 and hard disk 102.One source for the potential difference is the contact potential thatoriginates from the conducting portions of the slider body 101 and harddisk 102 having different work functions.

The work function of a material is the amount of energy that is neededfor releasing electrons from the surface of the material, and is relatedto the optical, electrical and mechanical properties of the material.When two materials having different work functions are brought together,electrons in the material having the higher work function tend to flowto the material having the lower work function. When the materials aremade into a parallel plate capacitor, equal and opposite surface chargesform on each material. The voltage formed between the plates of thecapacitor from these charges is referred to as a “contact potential.” Ina typical slider/disk interface, the conducting part of the slider body(e.g., 101) is sintered Al₂O₃-TiC and the conducting part of the disk(e.g., 102) is a cobalt based alloy magnetic layer. Even if the sliderand disk are both grounded, a potential difference can exist betweenthem due to the contact potential, which may generate an electrostaticforce greater than the van der Waals force.

As shown in FIG. 3, the respective work functions of the slider body andhard disk are further modified by overcoats and lubricants that aredeposited for tribology protection. In FIG. 3, hard disk 102 is coatedwith a carbon coating 102 a and a lubricant layer 102 b. As shown inFIG. 3, the mechanical spacing between hard disk 102 and slider body 101can be greater than the distance (e.g., 301) between slider body 101 andlubricant layer 102 b which is typically referred to as the “clearance”of slider body 101. The slider to disk clearance is typically defined bythe lowest point on the slider and the highest point on the disk. Hence,variations in the disk topography of disk 102 can affect the clearanceof slider body 101.

When in operation the rotation speed of disk 102 induces shear forceswhich can act upon lubricant layer 102 b causing it to separate fromcarbon coating 102 a. The lubricant layer 102 b can then migrate toother portions of disk 102 in an uneven manner which affects theclearance of slider body 101. Furthermore, this effect is enhanced dueto the electrostatic field of the slider/disk interface which tends todraw the lubricant into the slider/disk interface.

FIG. 4 shows a system for determining contact potential voltages andlocalized clearance data between a slider body and a hard disk of a harddisk drive in accordance with embodiments of the present invention. InFIG. 4, a computer 420 is coupled with a voltage adjuster 430 and anoptical range determining device 410. In embodiments of the presentinvention, optical range determining device 410 is a laser measuringdevice such as a laser interferometer, a laser Doppler vibrometer, anear-field solid immersion lens (SIL) device, etc. In operation, opticalrange determining device 410 is optically coupled with slider body 101and determines a distance thereto which can be used to determining theclearance change of slider body 101 relative to hard disk 102.

While the embodiment of FIG. 4 shows the use of a laser measuringdevice, embodiments of the present invention are well suited to utilizeother methods to determine the clearance change of slider body 101relative to hard disk 102. In one embodiment, the read back signalamplitude change is used to determine spacing change. The read backsignal amplitude vs spacing is described by the Wallace spacing equationwhich can be used to determine the clearance of slider body 101 relativeto hard disk 102. More specifically, the amplitude of the readbacksignal varies exponentially to the clearance of slider body 101. Thus,when slider body 101 is closer to hard disk 102 (e.g., at a reducedclearance), the amplitude of the readback signal will be greater thanwhen slider body 101 is further away from hard disk 102. In anotherembodiment of the present invention, the contact of slider body 101 canbe identified based on the Position Error Signal (PES) that is generatedin a well known manner.

In another embodiment, a change in capacitance between slider body 101and hard disk 102 is detected in response to a change in slider bodyclearance. For example, in embodiments of the present invention, sliderbody 101 is electrically isolated from suspension 106. As a result,system 400 effectively forms a capacitive loop and the slider bodyclearance will vary in response to changes in the voltage applied to theslider body/hard disk interface. A change in the capacitance (measuredat the slider body//hard disk interface can be detected and used todetermine the change in the slider body clearance.

In another embodiment, a change in the magneto-resistive resistance canbe detected and used to determine a change in the slider body clearance.For example, as the clearance of slider body 101 relative to hard disk102 decreases, the magneto-resistive resistance typically decreases dueto increased disk cooling. Alternatively, the magneto-resistiveresistance typically increases when contact between the slider body andhard disk occurs due to disk heating, thus causing an increase in thebaseline magneto-resistive modulation.

Voltage adjuster 430 is coupled with slider body 101 and is forgenerating a plurality of direct current (DC) pulses. In the embodimentof FIG. 4, voltage adjuster 430 comprises a pulse generator 431 and avoltage controller 432. It is noted that the components shown in FIG. 4are exemplary, and that in other embodiments of the present inventioncomputer 420 may be integrated with voltage adjuster 430 and/or opticalrange determining device 410.

In embodiments of the present invention, a first control measurement isdone without any voltages applied to the slider body. For example inrevolution 1 (e.g., 510 of FIG. 5) no voltage (e.g., 0 volts) is appliedbetween slider body 101 and hard disk 102 and the baseline readbacksignal amplitude is established. Concurrently, the voltage between theslider and disk is increased in small increments and the change in readback signal amplitude is noted and converted to spacing change. When theslider makes contact with the disk, further increase in the appliedvoltage will not cause further reduction in spacing and hence will notlead to further increase in read back signal amplitude. The clearancecan be estimated from the change of amplitude at contact to the initialread back signal amplitude with no voltage applied.

FIG. 5A shows exemplary bias voltages applied between a slider body anda hard disk in accordance with embodiments of the present invention. InFIG. 5A, a complete revolution of hard disk 102 is represented as wellas the bias voltages applied. It is noted that the bias voltagesrepresented in FIG. 5A are applied while slider body 101 is located overa single data track of hard disk 102. In revolution 1 (e.g., 510) novoltage is applied between slider body 101 and hard disk 102.Concurrently, a measurement of the clearance of slider body 101 is madeusing, for example, optical range determining device 410. Thismeasurement of the distance between slider body 101 and, for example,optical range determining device 410, provides a baseline measurementwhich will be used to determine a change in the clearance of slider body101 relative to hard disk 102 when various voltages are applied at theslider body/hard disk interface.

In revolution 2 (e.g., 520) a first set of positive bias voltages (e.g.,pulse 521 and pulse 522) are applied at between slider body 101 and harddisk 102. In the embodiment of FIG. 5A, pulse 521 and pulse 522 are onevolt direct current (DC) pulses. It is noted that in embodiments of thepresent invention another voltage (e.g., one half volt) may be applied.Furthermore, the duration (e.g., Pwidth) of pulse 521 and pulse 522 isselected to minimize contact between slider body 101 and hard disk 102should that occur. For example, in embodiments of the present invention,the pulse duration (e.g., Pwidth) is longer than the frequency of thepitch vibration of slider body 101 which is typically approximately 250kHz. Thus, in the embodiment of FIG. 5A, the Pwidth for pulse 521 andpulse 522 is approximately 50 microseconds. While the present embodimentonly shows two pulses per revolution of hard disk 102, it is appreciatedthat a greater or lesser number of pulses may be used in embodiments ofthe present invention. Thus, a variation in the clearance of slider body101 is determined relative to the baseline measurement of clearance whenno voltage is applied (e.g., 510).

In revolution 3 (530), a first set of negative bias voltages (e.g.,pulse 531 and pulse 532) are applied between slider body 101 and harddisk 102. In the embodiment of FIG. 5A, pulse 531 and pulse 532 are onevolt direct current (DC) pulses. Additionally, the duration (Pwidth) ofpulse 531 and pulse 532 is selected as described above. It is noted thatpulse 531 and pulse 532 are initiated such that they occur at thelocations of hard disk 102 that coincide with the location of previouslyapplied positive bias voltages 521 and 522 respectively. This can beaccomplished, for example, by timing the initiation of pulse 531 andpulse 531 relative to the spindle index of hard disk 102, or relative tosector/servo positioning information. In embodiments of the presentinvention, a change in the clearance of slider body 101 relative to thebaseline measurement (e.g., 510) is determined as described aboveconcurrent with the application of pulses 531 and 532.

In revolution 4 (540), a second set of positive bias voltages (e.g.,pulse 541 and pulse 542) are applied between slider body 101 and harddisk 102. In the embodiment of FIG. 5A, pulse 541 and pulse 542 are twovolt direct current (DC) pulses. Additionally, the duration (Pwidth) ofpulse 531 and pulse 532 is selected as described above. It is noted thatpulse 541 and pulse 542 are initiated such that they occur at thelocations of hard disk 102 that coincide with the location of previouslyapplied voltages (e.g., 521, 522, 531, and 532) respectively. Inembodiments of the present invention, a change in the clearance ofslider body 101 relative to the baseline measurement (e.g., 510) isdetermined as described above concurrent with the application of pulses541 and 542.

In revolution 5 (550), a second set of negative bias voltages (e.g.,pulse 551 and pulse 552) are applied between slider body 101 and harddisk 102. In the embodiment of FIG. 5A, pulse 551 and pulse 532 are twovolt direct current (DC) pulses. Additionally, the duration (Pwidth) ofpulse 551 and pulse 552 is selected as described above. It is noted thatpulse 551 and pulse 552 are initiated such that they occur at thelocations of hard disk 102 that coincide with the location of previouslyapplied voltage pulses 521, 522, 531, 532, 541, and 542, respectively.In embodiments of the present invention, a change in the clearance ofslider body 101 relative to the baseline measurement (e.g., 510) isdetermined as described above concurrent with the application of pulses551 and 552.

In another embodiment of the present invention, multiple DC pulses areapplied in successive revolutions of hard disk 102 at a given voltage todetermine an average variation in the clearance of slider body 101 atthat given voltage and at a specific discreet location. Referring now toFIG. 5B, in revolution 1 (e.g., 510), no bias voltage is applied betweenslider body 101 and hard disk 102. In revolution 2 (e.g., 520), positivebias voltages are applied as described above with reference to FIG. 5A.However, in successive revolutions of hard disk 102 (e.g., revolutions560, 570, 580), rather than increasing the voltage of the pulses and/orreversing the bias of them as was performed in FIG. 5A, the voltagepulses applied in revolution 2 (520) are repeated at the same locationwhile concurrently measuring the variation in the clearance of sliderbody 101 from the baseline measurement (e.g., 510). In so doing,embodiments of the present invention can account for variations in theclearance of slider body 101 relative to hard disk 102 due to vibrationof the slider body caused by, for example, aerodynamic forces acting onthe HGA. In other methods, a single pulse of longer duration is used todetermine changes in the clearance of the slider body. Because of thelonger duration of the pulse, the measurement of the clearance of theslider body does not account for vibration of the slide body. Thus,embodiments of the present invention determine variations in theclearance of slider body 101 in response to changes in the biasing ofthe slider/hard disk interface more precisely than conventional methods.

As shown in FIGS. 5A and 5B, embodiments of the present invention mayalso facilitate simultaneously determining localized contact potentialvoltages and localized clearance data between slider body 101 and harddisk 102. In embodiments of the present invention, the voltage of the DCpulses applied between slider body 101 and hard disk 102 are increaseduntil a contact between them is detected, which facilitates determiningthe absolute clearance of slider body 101 relative to hard disk 102 at agiven voltage. In conventional methods, the use of long duration voltagepulses increases the likelihood of damage to the slider body and/ormagnetic read/write transducer due to extended contact with the harddisk. However, in embodiments of the present invention, this contact isreduced due to the shorter duration (e.g., Pwidth) of the DC pulses.

Additionally, because of the short duration of the voltage pulses,multiple discreet portions of a data track of hard disk 102 can bemeasured. Conventional clearance measurement methods, which typicallyutilize much longer bias signals (e.g., 10-20 Hz, or even multipleseconds of continuous DC), measure contact potential and/or diskclearance over numerous revolutions of the hard disk when the bias isapplied, thus resulting in the measurement of entire data tracks.Another conventional method applies a constant voltage between theslider body and the hard disk over multiple revolutions of the harddisk. The amplitude of a readback signal is then sampled as the harddisk revolves. Furthermore, the method is performed over larger segmentsof the data track, resulting in less precise measurement due to noise.As a result, circumferential variations due to disk microwaviness cannot be resolved with other methods as with the present invention. Thesevariations in surface topography of the disk (e.g., micro-waviness,roughness, and/or texture) can also cause variations in the contactpotential over different locations on the disk which cannot be preciselymapped using the longer voltage pulses of the conventional art.Additionally, the longer voltage bias used in conventional methodsincreases the likelihood of lubricant migration and of particles beingdrawn into the slider/disk interface and causing damage. In the presentinvention, the shorter duration of the voltage pulses, as well as theuse of positive and negative voltage pulses, reduces the risk ofcharging the slider/hard disk interface. Thus, there is less likelihoodof lubricant migration and/or drawing particles to the slider/hard diskinterface in embodiments of the present invention. Furthermore, byapplying the same voltage numerous times over the same portion of harddisk 102 and deriving a corresponding average variation in theclearance, a more accurate measurement of the contact potential and/ordisk clearance at that discreet location of the hard disk is possiblethan in conventional methods.

FIGS. 6A and 6B are graphs showing variations in the clearance of aslider body relative to a hard disk in response to variations in anapplied bias voltage in accordance with embodiments of the presentinvention. In FIG. 6A, a positive DC voltage pulse of 1 volt (e.g.,pulse 521 of FIG. 5A) causes the clearance of slider body 101 to dropapproximately 0.1 nanometer relative to when no voltage pulse is applied(e.g., 510 of FIG. 5A). When a negative DC voltage pulse of 1 volt(e.g., pulse 531 of FIG. 5A) is applied, the clearance of slider body101 rises approximately 0.2 nanometers relative to the clearance ofslider body 101 when no voltage pulse is applied (e.g., 510 of FIG. 5A).A positive DC voltage pulse of 2 volts (e.g., pulse 541 of FIG. 5A)causes the clearance of slider body 101 to drop 0.6 nanometers relativeto the clearance of slider body 101 when no voltage pulse is applied(e.g., 510 of FIG. 5A). A negative DC voltage pulse of 2 volts (e.g.,pulse 551 of FIG. 5A) causes the clearance of slider body 101 to dropapproximately 0.2 nanometers relative to the clearance of slider body101 when no voltage pulse is applied (e.g., 510 of FIG. 5A). In FIG. 6Athe plot of the clearance of slider body 101 is continued through avoltage of +5 volts DC and −5 volts DC. It is noted that in FIG. 6A, theclearance of slider body 101 reaches a peak at approximately −1 volt.This indicates that the contact potential voltage is approximately 1volt. Subsequently, during normal operation of hard disk drive 100, abias of −1 volt can be applied to the interface of slider 101 and harddisk 102 to eliminate the contact potential voltage.

In FIG. 6B, a positive DC voltage pulse of 1 volt (e.g., pulse 521 ofFIG. 5A) causes the clearance of slider body 101 to drop approximately0.2 nanometers relative to when no voltage pulse is applied (e.g., 510of FIG. 5A). When a negative DC voltage pulse of 1 volt (e.g., pulse 531of FIG. 5A) is applied, the clearance of slider body 101 relative tohard disk 102 rises approximately 0.1-0.2 nanometers relative to theclearance of slider body 101 when no voltage pulse is applied (e.g., 510of FIG. 5A). A positive DC voltage pulse of 2 volts (e.g., pulse 541 ofFIG. 5A) causes the clearance of slider body 101 to drop 0.7-0.8nanometers relative to when no voltage pulse is applied (e.g., 510 ofFIG. 5A). A negative DC voltage pulse of 2 volts (e.g., pulse 551 ofFIG. 5A) causes no significant change in the clearance of slider body101 relative to when no voltage pulse is applied (e.g., 510 of FIG. 5A).In FIG. 6B the plot of the clearance of slider body 101 is continuedthrough a voltage of +5 volts DC and −5 volts DC. Again, it is notedthat in FIG. 6B, the clearance of slider body 101 reaches a peak atapproximately −1 volt. This indicates that the contact potential voltageis approximately 1 volt. Subsequently, during normal operation of harddisk drive 100, a bias of −1 volt can be applied to the interface ofslider 101 and hard disk 102 to eliminate the contact potential voltage.

Additionally, the maximum drop in the clearance of slider body 101occurs when a bias of +3 volts DC is applied. This indicates that sliderbody comes into contact with hard disk 102 when a positive bias of +3volts DC is applied. A similar effect is exhibited when a bias of −3volts DC is applied. It is noted that there is a difference in maximumdrop in the clearance when a positive or negative voltage is applied.This maybe caused by lube pooling between the slider and disk at thehere exemplary slider disk combination which had a fairly thick lubefilm of 12 Angstrom Z-tetraol lubricant. This effect is minimized withreduced humidity and highly bonded lubricant. When biases of ±4 voltsand ±5 volts are applied, slider body 101 exhibits a smaller drop in theclearance relative to hard disk 102.

FIG. 7 is a graph showing a change in voltage supply when a slider bodycontacts the hard disk. In embodiments of the present invention, acontact between slider body 101 and hard disk 102 is detected bydetecting a change in current. For example, in embodiments of thepresent invention, slider body 101 is electrically isolated fromsuspension 106 which is left at ground level. Slider body is directlycoupled with a voltage source (e.g., voltage adjuster 430 of FIG. 4) andthe electrical bias is applied to the slider/hard disk interface asdescribed above. In embodiments of the present invention, the currentsupplied by voltage adjuster 430 is limited so that if the current limitis exceeded, the voltage pulse breaks down before damaging theinterface. In embodiments of the present invention, voltage adjuster 430is limited to providing current in the micro amp range or less. Lowcurrent sources will limit damage to the interface and cause immediatevoltage breakdown at the faintest slider disk contact.

In FIG. 7, slider body 101 contacts hard disk 102 when a bias of 5 voltsis applied. In regions 701 and 702, a breakdown in the voltage occurs,because the voltage adjuster 430 has been limited to supply no more than2 milli-amps of current. When contact between slider body 101 and harddisk 102 occurs, voltage adjuster 430 cannot exceed 2 milli-amps ofcurrent and the voltage breakdown occurs.

It is noted that embodiments of the present invention may use othermethods for detecting contact between slider body 101 and hard disk 102.However, monitoring current output from voltage adjuster 430 istypically more precise. For example, embodiments of the presentinvention may monitor the voltage supplied to the slider/hard diskinterface, use a piezo-electric pressure sensor to monitor themechanical pressure, and/or vibrations, acting upon slider body 101, oran acoustic monitor may be coupled with slider body 101 to detect whencontact occurs. In anther embodiment, contact is indicated when the readback amplitude signal does not further increase with increased appliedvoltages. In another embodiment, contact is indicated when an increasein servo position error signal off-track vibrations are detected.Alternatively, an increase in the baseline magneto-resistive modulationindicates a contact between slider body 101 and hard disk 102. Thus,embodiments of the present invention can detect contact between sliderbody 101 and hard disk 102 more precisely than conventional methods andcan minimize the duration of that contact.

FIG. 8 is a flowchart of a method 800 for measuring contact potential ina hard disk drive using positive and negative electrical pulses inaccordance with embodiments of the present invention. In step 810 ofFIG. 8, at least one positive direct current (DC) pulse is appliedbetween slider body 101 and hard disk 102. As described above withreference to FIGS. 5A and 5B, embodiments of the present invention applyshort duration DC pulses between slider body 101 and hard disk 102. Inembodiments of the present invention, at least one positive directcurrent (DC) pulse is applied. As shown in FIGS. 6A and 6B, a pluralityof positive direct current (DC) pulses are applied with increasedvoltage. This facilitates determining contact potential voltage andslider body clearance relative to hard disk 102. Because of the shortduration of these pulses, embodiments of the present invention candetermine the contact potential voltage and/or disk clearance atdiscreet locations of the hard disk which are only portions of a datatrack of hard disk 102.

In another embodiment of the present invention, it is possible to applya continuous voltage (e.g., positive and/or negative voltage) betweenslider body 101 and hard disk 102 and measure the read back signalamplitude at different sectors of the disk, thereby measuring clearanceat different locations within one revolution. However, using a longcontinuous pulse may increase the likelihood of lubricant pickup on theslider air bearing surface.

In step 820 of FIG. 8, at least one negative direct current (DC) pulseis applied between the slider body and the hard disk. In embodiments ofthe present invention, at least one negative direct current (DC) pulseis applied between slider body 101 and hard disk 102 as well as thepositive direct current (DC) pulse of step 810. As shown in FIGS. 6A and6B, a plurality of negative direct current (DC) pulses are appliedbetween slider body 101 and hard disk 102 with increasing voltage.Again, this facilitates determining contact potential voltage betweenslider body 101 and hard disk 102.

In step 830 of FIG. 8, a contact potential voltage is determined betweenthe slider body and the hard disk in response to applying the at leastone positive direct current (DC) pulse and the at least one negativedirect current (DC) pulse. Referring again to FIGS. 6A and 6B, theclearance of slider body 101 reaches a peak at approximately −1 volt.This indicates that the contact potential voltage is approximately 1volt. Subsequently, during normal operation of hard disk drive 100, abias of −1 volt can be applied to the interface of slider 101 and harddisk 102 to eliminate the contact potential voltage. In conventionalmethods, prolonged biasing (e.g., either positive or negative charges)of the slider body/hard disk interface can cause migration and poolingof the lubricant layer in the interface. Embodiments of the presentinvention advantageously utilize both positive and negative electricalpulses to reduce biasing of the slider body/hard disk interface and thusreduce migration and pooling of the lubricant layer.

The preferred embodiment of the present invention, measurement ofcontact potential in a magnetic disk drive using positive and negativeelectrical pulses, is thus described. While the present invention hasbeen described in particular embodiments, it should be appreciated thatthe present invention should not be construed as limited by suchembodiments, but rather construed according to the following claims.

1. A method for measuring contact potential in a hard disk drive, saidmethod comprising: applying at least one positive direct current (DC)pulse between said slider body and a hard disk of said hard disk drive;applying at least one negative direct current (DC) pulse between saidslider body and said hard disk; and determining a contact potentialvoltage between said slider body and said hard disk in response toapplying said at least one positive direct current (DC) pulse and saidat least one negative direct current (DC) pulse, wherein said at leastone positive direct current (DC) pulse and said at least one negativedirect current (DC) pulse are each applied at a same location on saidhard drive.
 2. The method as recited in claim 1 further comprises:applying said at least one positive direct current (DC) pulse betweensaid slider body and a discrete location of said hard disk; and applyingsaid least one negative direct current (DC) pulse between said sliderbody and said discrete location.
 3. The method as recited in claim 1further comprising: applying at a discrete location a plurality ofpositive direct current (DC) pulses between said slider body and saidhard disk; and applying at said discrete location a plurality ofnegative direct current (DC) pulses between said slider body and saidhard disk.
 4. The method as recited in claim 3 wherein said determininga contact potential voltage further comprises: deriving a first averageclearance change of said slider body corresponding to said plurality ofpositive direct current (DC) pulses; deriving a second average clearancechange of said slider body corresponding to said plurality of negativedirect current (DC) pulses; and determining said contact potentialvoltage based upon a maximum clearance change of said slider bodyrelative to said hard disk.
 5. The method as recited in claim 4 furthercomprising: determining said first average clearance change and saidsecond average clearance change of said slider body using an opticalrange determining device.
 6. Amended) The method as recited in claim 4further comprising: determining said first average clearance change andsaid second average clearance change of said slider body by sensing avariation in the amplitude of a readback signal at said discretelocation.
 7. The method as recited in claim 3 further comprising:increasing the voltage of said plurality of positive direct current (DC)pulses and said plurality of negative direct current (DC) pulses until acontact between said slider body and said hard disk occurs; anddetecting a change in the current flow between said slider body and saidhard disk when said contact occurs.
 8. A system for determininglocalized contact potential voltages and localized clearance databetween a slider body and a hard disk of a hard disk drive comprising: ahousing; a disk pack mounted to said housing and comprising said harddisk that is rotatable relative to said housing, the disk pack definingan axis of rotation and a radial direction relative to the axis; aslider body mounted to said housing and disposed proximate to said harddisk; a potential voltage adjuster coupled with said slider body andwith said hard disk, said potential voltage adjuster for generating andcontrolling the voltage of a plurality of direct current (DC) pulsesapplied at a same location on said hard disk and comprising: a directcurrent (DC) pulse generator; and a direct current (DC) voltagecontroller; a processor coupled with said voltage adjuster; and adetector coupled with said slider body and with said processor.
 9. Thesystem of claim 8 wherein said processor determines an average clearancechange of said slider body in response to a plurality of positive directcurrent (DC) pulses and a plurality of negative direct current (DC)pulses generated by said voltage adjuster.
 10. The system of claim 8wherein said voltage adjuster generates a plurality of direct current(DC) pulses at a pre-designated voltage between said at least one diskand said slider body.
 11. The system of claim 8 wherein said processorcauses said voltage adjuster to generate said plurality of positivedirect current (DC) pulses and said plurality of negative direct current(DC) pulses at said discrete location of said hard disk, and whereinsaid discrete location comprises a portion of a data track.
 12. Thesystem of claim 8 wherein said detector comprises an optical rangedetermining device.
 13. The system of claim 8 wherein said detectorcomprises a component for sensing a variation in the amplitude of areadback signal at said same location of a data track of said hard disk.14. The system of claim 8 further comprising: a contact detector fordetecting a contact between said slider body and said hard disk inresponse to an increase in the voltage generated by said direct current(DC) voltage adjuster.
 15. A system comprising: a disk pack comprisingat least one hard disk; a slider body disposed proximate to said harddisk; a generating means for generating at least one positive directcurrent (DC) pulse and at least one negative direct current (DC) pulsebetween said hard disk and said slider body, wherein said at least onepositive direct current (DC) pulse is generated at a discrete locationon said hard disk and wherein said at least one negative direct current(DC) pulse is generated at said discrete location; a controlling meansfor controlling said generating means and for determining a contactpotential voltage in response to said generating said at least onepositive direct current (DC) pulse and said at least one negative directcurrent (DC) pulse.
 16. The system of claim 15 wherein said generatingmeans further comprises: a direct current pulse generator for generatingsaid at least one positive direct current (DC) pulse at said discretelocation and for generating said at least one positive direct current(DC) pulse at said discrete location; and a voltage controller forcontrolling the voltage of said plurality of direct current (DC) pulses.17. The system of claim 15 further comprising: a detecting means fordetecting a contact between said slider body and said hard disk.
 18. Thesystem of claim 15 further comprising: a measuring means for measuring aclearance change of said slider body.
 19. The system of claim 18 whereinsaid controlling means is further for determining an average clearancechange of said slider body in response to said at least one positivedirect current (DC) pulse and said at least one negative direct current(DC) pulse and for determining said contact potential voltage based uponsaid average clearance change of said slider body.
 20. The system ofclaim 15 wherein said controlling means is further for controlling saidgenerator wherein said at least one positive direct current (DC) pulseand said at least one negative direct current (DC) pulse are generatedwhen said slider body is proximate to said discrete location of saidhard disk comprising a portion of a data track.